The present invention is generally related to mechanical coupling, and, more particularly, the present invention is related to elastomeric joints that may be configured to couple devices, such as steering linkages in railway vehicles.
In a railway vehicle, such as a locomotive, the vehicle body is mounted on a frame which in turn is mounted on a pair of longitudinally spaced apart multi-axle trucks having wheels which ride on the rails of a train track. The two trucks are typically identical, with each truck having typically two or three axles and a pair of wheels on opposite ends thereof. In an exemplary three axle diesel-electric locomotive, each axle further includes an integral electrical motor combination, or simply motor combo, for directly powering the wheels. The motor combos drive the wheels for propelling the locomotive either in forward or reverse directions utilizing inherent traction friction between the wheels and the rails. The locomotive, in turn, pulls or pushes a train of railway cars joined thereto. The trucks also include conventional brakes for stopping the locomotive again using the inherent traction friction between the wheels and the rails. Accordingly, traction loads must be carried between the axles and the frame during forward and reverse driving and braking operation. This is conventionally accomplished by suitably suspending the axles to the frame.
One important consideration in locomotive design is the ability of the axles to negotiate curves during operation. In a multi-axle truck, the leading axle negotiates a turn before the trailing axle which creates substantial lateral loading, e.g., steering loads, between the axles and the frame and affects efficient operation and longevity of the trucks. In order to accommodate typical problems associated with negotiating rail curves, self-steering trucks have been developed. Steering is accomplished by suitably interconnecting the leading and trailing axles so that the axles yaw in opposite directions to each other upon negotiating curves.
Axle suspension design is generally complex due to various mechanical considerations: the axles should be vertically suspended from the frame for accommodating vertical loads; the axles should be longitudinally constrained for carrying the forward and reverse traction loads to the frame; the axles should be also mounted for allowing self-steering yaw motion thereof in opposite angular directions between leading and trailing axles; and, the axles should be laterally constrained. Axle suspension in a three-axle truck may be further complicated since the leading and trailing end axles need to be angularly interconnected for self-steering, and the middle axle is independent from the leading and trailing end axles and is interposed longitudinally between such axles.
U.S. patent application No. 6,006,674, commonly assigned to the same assignee of the present invention, discloses an improved design over self-steering trucks that have undesirably included a large number of pivoting joints, which are typically made using conventional bearings or friction joints, and are thus susceptible to wear and fretting problems. It is desirable, however, to further improve the self-steering linkage by providing a multi-degree of freedom elastomeric joint that allows to further reduce the number of components subject to undesirable wear and still meet the complex mechanical constraints required by such self-steering linkage.
Generally speaking, the present invention fulfills the foregoing needs by providing in one aspect thereof, a multi-degree of freedom elastomeric joint that in fictionless engagement allows differential longitudinal and pivotal movement between adjoining ends of a pair of reaction arms used in a steering linkage of a railway truck.
In one exemplary embodiment, the joint comprises a wing plate that includes a base plate generally extending along a first axis and generally perpendicular to a second axis. The wing plate further includes a mutually opposite first and second bushing-receiving bores co-axially aligned relative to a third axis perpendicular to said first and second axes. A plurality of elastomeric shear pads is affixed on mutually opposite sides of the base plate. The plurality of shear pads is stacked generally perpendicular to the second axis. Top and bottom elastomeric bushings are received by said respective bushing-receiving bores. Each elastomeric bushing comprises a plurality of torsion pads and includes a respective pin-receiving bore. Each of the shear pads and torsion pads comprises a plurality of alternating layers of resilient and nonextensible materials, wherein the shear pads are compressed, e.g., compressively preloaded during installation, to provide stiff opposition to forces along said second axis, while accommodating differential displacement along the first axis and/or along the third axis by providing relatively low stiffness along such first and/or second axes, and wherein the torsion pads are compressed, e.g., compressively preloaded during installation, to enable pivotal movement about the third axis by providing relatively low torsional stiffness about that third axis while providing stiff opposition to radial forces on the torsion pads.
The present invention further fulfils the forgoing needs by providing in another aspect thereof, a method of assembling an elastomeric joint. The method allows for providing a wing plate that includes a base plate generally extending along a first axis and generally perpendicular to a second axis. The wing plate further provides mutually opposite first and second bushing-receiving bores co-axially aligned relative to a third axis perpendicular to the first and second axes. The method allows for affixing a plurality of elastomeric shear pads on mutually opposite sides of the base plate. The plurality of shear pads is stacked generally perpendicular to the second axis. A fitting step allows for interferingly fitting top and bottom elastomeric bushings in the respective bushing-receiving bores. Each elastomeric bushing comprises a plurality of torsion pads and includes a respective pin-receiving bore. Each of the shear pads and torsion pads comprises a plurality of alternating layers of resilient and nonextensible materials. Respective preloading steps respectively allow for compressively preloading the shear pads to provide stiff opposition to forces along the second axis, while accommodating differential displacement along the first axis and/or along the third axis, and for compressively preloading the torsion pads to enable pivotal movement about the third axis while providing stiff opposition to radial forces on the torsion pads.